1. Field of the Invention
This invention relates to lubricated tinplate container stock for use in the fabrication of seamless container bodies by the drawing and ironing process.
2. Description of the Prior Art
The fabrication of seamless metal container bodies by the drawing and ironing method is well known in the art. Such a method first involves drawing a metal blank into a shallow cup, i.e. "cupping" by forcing the blank through one or more drawing dies and then while supporting the drawn cup on a punch, passing the cup through one or more ironing dies, the inside diameters of which are progressively smaller, thus resulting in the thinning and elongation of the sidewalls of the cup. Because of the severe stress placed on the metal blank in such operations, a lubricant is required to allow the metal to flow more smoothly during the drawing and ironing, thus more uniformly distributing the stresses and avoiding the tearing or galling which could otherwise occur. Such lubrication is most important during the ironing stage where it also acts as a coolant, but some amount of surface lubricant is needed on tinplate during the initial cupping operation. Consequently, it is customary to apply a concentrated form of the lubricant/coolant to the blanks just prior to cupping.
A variety of lubricants have been developed for such purposes and they are well known in the art. For example, U.S. Pat. No. 3,873,458 describes the application of a combined resin and oil lubricant from an aqueous dispersion or emulsion while U.S. Pat. No. 3,994,252 discloses the use of a pre-annealing rinse including MnSO.sub.4 which when subsequently dried forms an MnS lubricant coating on steelplate.
Notwithstanding the prior art use of lubricants in drawing and ironing operations, galling problems persist with some frequency and overheating of the tooling is a common occurrence. Equally objectionable are the surface scratching and "tin wipe" imperfections commonly experienced in such drawing and ironing operations. "Tin wipe" is a condition characterized by an unsightly frosted area on the sidewall of an otherwise bright reflective container. These problems have been virtually overcome by the present invention which will be described in greater detail below.